This application claims the priority of German Application No. 196 31 215.9, filed in Germany on Aug. 2, 1996, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an eversible tube for motor vehicles, and more particularly to an eversible tube used as a steering shaft, or as a connecting part between portions of a steering shaft.
German patent document DE 1 931 844 B1, relates to an eversible tube for motor vehicles, intended to absorb an axial impact as a result of the eversion process. Following the initiation of the eversion movement, a continuous plastic deformation is provided in this case that is achieved by a shape which has a constant wall thickness and which is cylindrical over its entire length.
In German patent document DE 33 21 198 C1, a safety steering shaft made of plastic is described, said shaft having sections with different outside diameters while the inside diameter remains constant, with a portion being provided for yielding deformation during axial loading.
This section is made with a larger outside diameter and a smaller wall thickness and can expand under pressure. It is not possible with this device to achieve a reduction of energy of the same order of magnitude as in a design that uses an eversible tube. The resistance to deformation decreases with increasing deformation accompanied by the breakup of the fiber structure of the plastic steering shaft.
A goal of the present invention is to suitably adapt the deformation resistance of an eversible tube in a steering shaft in order to better accept the force of an impact by a passenger.
This and other goals have been achieved according to the present invention by providing an eversible tube for a steering shaft of a motor vehicle, said tube being eversible to absorb energy of an axial force applied thereto by plastic deformation, said tube comprising at least two longitudinal sections which are plastically deformable by respectively different values of said axial force.
An eversible tube provided as a connecting part between two sections of a steering shaft of a motor vehicle, during axial loading of the steering wheel during a vehicle collision, can decrease the forces imposed by the passenger on the steering shaft due to its ability to deform and thus reduce the load imposed on the passenger by the resistance of the steering shaft. For this purpose, one end of the eversible rod is pushed through the cavity in the eversible tube or everted outward, with the wall of the eversible tube undergoing continuous deformation.
The eversible tube according to the invention reacts to the impact of the passenger appropriately, in that it has along its length areas with different degrees of resistance to deformation that determine the extent of deformability of the eversible tube.
The eversible tube is designed so that, beginning at the end where the eversion movement begins, it has a longitudinal section adjoined by a longitudinal section with at least one of (a) a narrower inside diameter or (b) a thicker wall, so that the eversible tube can be everted with less resistance in the first longitudinal section and with greater resistance in the second longitudinal section. The resistance to deformation of the eversible tube is selected and designed such that a lighter individual will be stopped by the flexibility of the steering shaft in the vicinity of the first, lower resistance, while a heavier individual will also reach the area with greater resistance and, following the more flexible phase, will be restrained with a greater resistance by the steering shaft in order to avoid complete eversion of the eversible tube and to prevent the steering shaft from striking the end stop.
A longitudinal section with easier deformability can in turn abut this longitudinal section with a greater resistance to deformation, so that the load imposed by the passenger decreases again, which then in the possible eversion phase will close off the section with the higher resistance to deformation.
An eversible tube with adjoining diameters of different sizes can be made with a wall thickness which is approximately constant over its length or which varies, so that the resistance to deformation of the eversible tube can additionally be influenced. Similarly, the eversible tube can be adapted simply on the basis of changing the wall thickness to be deformed over its length to suit the desired deformation conditions. The wall thickness can also be changed by separate parts that are attached to the eversible tube. The flexibility of the steering shaft during an axial application of force can thus be simply adapted to conditions in any motor vehicle.
A deformation force that remains approximately constant over a longitudinal section of the eversible tube, i.e., a resistance of the steering shaft to the passenger applies a force that is approximately at the same level, is achieved by each cylindrical shape of this section. The cylindrical sections that differ in diameter can be joined by conical sections that produce a smooth transition from low deformation resistance to high deformation resistance.
To support the steering shaft with the eversible tube, a three-point bearing with axially spaced bearing positions is advantageous, whose central bearing position locates the steering shaft near the eversible end of the eversible tube axially displaceably, so that the steering shaft does not kink during the deformation of the eversible tube. In order for the longitudinal displaceable portion of the steering shaft to be guided smoothly during its axial displacement movement, a sliding bearing location has a ball cage that is displaceable in it with the steering shaft. The bearing points can be combined integrally into a single mounting flange in order to be commonly supported in the motor vehicle.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.